RECOVERY OF MOLYBDENUM AND VANADIUM FROM SPENT HYDRODESULFURIZATION CATALYSTS BY MEANS OF LIQUID-LIQUID-EXTRACTION

The total dissolution in sulfuric acid of spent hydrodesulfurization catalysts results in an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt and nickel as well as a large excess amount of aluminum. In the present work, the fundamental extraction characteristics of these metals from the sulfuric acid media with some typical commercial acidic organophosphorus compounds such as TR-83, PC-88A and CYANEX 272 have been investigated to develop an extraction process for the recovery of molybdenum and vanadium from the solution of the total dissolution. The experimental results demonstrated that CYANEX 272 was suitable for selectively separating and recovering molybdenum and vanadium over the other metals involved in the sulfate solutions at comparatively low pH. An elemental recovery processing route was proposed. Molybdenum was recovered by extracting with 40% CYANEX 272 in EXXSOL D80 from the sulfuric solution at pH 1.5, and by stripping with 6% NH4OH solution after the co-extracted iron and vanadium were scrubbed from the loaded solvent with a moderate concentration of H2SO4 solution. Vanadium in the scrub solution was further recovered by again extracting with the same extractant after the pH was adjusted to 1.5 with Ca (OH)(2) powder and by stripping with 6% NH4OH solution.